As a semiconductor wafer has been thinner and thinner, instead of a method of segmenting a semiconductor wafer into a plurality of chips using a cutting tool such as a blade or the like, where there may occur defects or cracks in the semiconductor wafer, which may lead to low yield, a plasma etching method has recently attracted a great attention. In this plasma etching method, a semiconductor wafer whose circuit forming side is attached with a protective sheet is hermetically sealed in a plasma treating chamber and is segmented into a plurality of chips by subjecting the semiconductor wafer to plasma etching from other side of the semiconductor wafer, the protective sheet serving to prevent the chips from being dispersed and protect circuits (see Patent Document 1).    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2005-191039